Plug-in hybrid electric vehicles (PHEV), which use both electric motors and engines, and electric vehicles (EV), which do not have engines and are driven by electric motors, are coming into wide use. Vehicles such as plug-in hybrid electric vehicles and electric vehicles have batteries for storing power to drive the electric motors, and the batteries are charged using external charging stations.
Methods for charging batteries for driving motors include AC charging and DC charging. DC charging methods include CHAdeMO and CCS (Combined Charging System; also called Combo). A charging station conforming to CHAdeMO has a DC charging connector, and communicates with the vehicle through a CAN (Controller Area Network). Meanwhile, a charging station conforming to Combo has a DC charging connector and an AC charging connector, checks connection to a vehicle, completion of charging preparation, the charging state, and the like using control pilot (CPLT) signals that are transmitted and received through a communication line, and controls power supply. This charging station also performs PLC communication, in which other control signals are superimposed on the control pilot signals, to transmit and receive various kinds of information associated with charging to and from the vehicle and the charging station.
Since there are two DC charging methods, if the method employed by the charging station does not match the method employed by the vehicle, a situation where charging cannot be performed may occur. JP 2014-124034A and JP 2014-124033A disclose relay devices that convert and relay the type of control signals associated with charging between a vehicle and a charging station that conform to different DC charging methods, thereby realizing battery charging using the charging station with a different charging method at a low cost.
However, although the relay devices according to Patent Documents 1 and 2 enable control signals to be normally transmitted and received between the vehicle and the charging station, these relay devices cannot prevent the occurrence of an abnormal current such as a reverse current or rush current caused by a potential difference between a battery voltage and a DC voltage output by the charging station.
The present invention has been made in view of the foregoing situation, and aims to provide a vehicle-mounted charging system that enables a vehicle battery to be charged and prevent an abnormal current from occurring between the vehicle and a charging station, regardless of which charging method is employed by the charging station.